The present invention is directed to bicycle transmissions and, more particularly, to an internally mounted multi-speed hub transmission for a bicycle.
An internally-mounted multi-speed hub transmission sometimes is mounted to the rear wheel of a bicycle so that the rider can select different gear ratios to vary the pedaling effort. A typical hub transmission includes a hub axle that is mounted to the bicycle frame, a driver rotatably supported to the hub axle for receiving the pedaling force through a sprocket and chain, and a hub shell rotatably supported to the hub axle. A power transmitting mechanism is disposed between the driver and the hub shell for communicating rotational power from the driver to the hub shell through a plurality of power transmission paths, wherein each power transmission path typically produces a unique gear ratio. The power transmitting mechanism ordinarily comprises a planetary gear mechanism including one or more sun gears rotatably supported around the hub axle, a ring gear rotatably supported around the hub axle, a planet gear carrier rotatably supported around the hub axle, and a plurality of planet gears rotatably supported to the planet gear carrier and meshing with the sun gear and the ring gear. The plurality of power transmission paths and the corresponding gear ratios are selected by selectively nonrotatably coupling the various components to each other. For example, one gear ratio may be selected by nonrotatably coupling a sun gear to the hub axle, another gear ratio may be selected by nonrotatably coupling the driver relative to the planet gear carrier, and another gear ratio may be selected by nonrotatably coupling the driver relative to the ring gear. Many such coupling relationships often are possible in a typical hub transmission, thus resulting in a relatively large number of possible gear ratios.
When a gear ratio is selected by nonrotatably coupling the sun gear to the axle, the coupling may be accomplished by a ratchet and pawl mechanism disposed between an inner peripheral surface of the sun gear and the hub axle. More specifically, a plurality of pawls may be mounted to the inner peripheral surface of the sun gear such that an end of each pawl is biased radially inwardly by a spring. The outer peripheral surface of the hub axle typically forms a plurality of ratchet teeth or abutments which engage the ends of the pawls to nonrotatably couple the sun gear to the hub axle, and a control sleeve is rotatably supported to the hub axle to selectively expose the abutments. As a result, the sun gear is free to rotate relative to the hub axle when the abutments are covered by the control sleeve, and the sun gear is nonrotatably coupled to the hub axle when the abutments are exposed.
The sun gears usually are supported to the hub axle through the plurality of pawls. As a result, often there is some looseness in the support of the sun gear on the hub axle which decreases the precision of the ratchet and pawl mechanism. Such looseness can be compensated for by increasing the number of pawls, but that increases the cost and complexity of the transmission, not to mention the risk of malfunction. Additionally, the circumferential distance between successive ratchet teeth or abutments on the hub axle ordinarily is relatively large. As a result, the sun gear ordinarily must rotate a substantial distance before the pawls engage the ratchet teeth or abutments. This causes undesirable delay in the gear switching operation.
Another type of hub transmission includes a sun gear rotatably mounted around the axle, wherein an inner peripheral surface of the sun gear defines a plurality of ratchet teeth. One or more pawls may be disposed in an aperture formed in a hollow axle to selectively engage the plurality of ratchet teeth. However, a hollow axle is not very strong and is not suitable for severe operating conditions. Yet another type of hub transmission also uses pawls mounted to the axle, but the pawls are operated by a control sleeve that directly supports the sun gears. Such a configuration causes excessive friction on the control sleeve.
Another disadvantage of conventional hub transmissions is that, when switching from one gear ratio to another gear ratio, the transmission sometimes must pass temporarily through another gear ratio that is not near the destination gear ratio as the various components change their coupling relationships. This phenomenon is discussed more fully in the detailed description below. For example, when shifting from a small gear ratio, wherein the hub shell rotates around the axle at a relatively slow rate relative to the driver, to a higher gear ratio, wherein the hub shell rotates around the axle at a larger rate relative to the driver (such as occurs when the bicycle is decelerating), the transmission may temporarily switch into a gear ratio that is lower than the original gear ratio. This causes the pedals to speed up temporarily, which is opposite the desired effect and can be very disconcerting to the rider.
Another disadvantage of conventional hub transmissions is that the sun gear ratchet and pawl mechanisms ordinarily are controlled by a relatively thin sleeve that is rotatably supported on the hub axle. As noted above, such a sleeve often is used to selectively expose the abutments on the hub axle for engaging the pawls on the sun gears. The sleeve typically is relatively long and is operated from outside the hub shell, thus creating significant torsional stresses on the sleeve. Such forces create a risk of bending or twisting the sleeve.
Another disadvantage of conventional hub transmissions is that the sleeve that controls the ratchet and pawl mechanisms (and any other desired coupling mechanisms) is sometimes coupled to an external actuating member such as an actuating ring through one or more return springs that bias the actuating ring to a start position. Such a biasing force is used not only to provide proper tensioning of the components during the switching operations but also to help control a shift assist function. Such a shift assist function uses the force of the rotating driver to help overcome resistance to the shift operation such as occurs when significant pedaling force is applied to the hub. More specifically, a coupling mechanism that is normally biased to an inoperative state is activated to couple the sleeve to the driver so that the force from the driver overcomes the excessive resistance. In any event, when such a biased actuating ring is operated by a battery-operated motor, the motor must overcome the biasing force of the return spring. This typically requires a relatively large motor that consumes a substantial amount of power, thus significantly reducing battery life.
The present invention is directed to a bicycle hub transmission wherein the sun gears are stably supported on the hub axle, wherein the gear switching operation is performed with precision and minimal delay and with minimal effect on the rider, wherein components such as the control sleeve used to control a ratchet and pawl mechanism is stably supported to minimize the risk of bending or other damage, and wherein the actuating member used for the gear switching operation does not cause excessive power consumption when driven by a battery-operated motor.
In one embodiment of the present invention directed to a basic sun gear apparatus, the sun gear apparatus includes an axle, a sun gear rotatably supported around the axle, and a sun gear guide ring disposed between an inner peripheral surface of the sun gear and the axle. The sun gear guide ring minimizes or eliminates looseness in the coupling between the sun gear and the axle. One or more such guide rings may be used to support a single sun gear, or one guide ring may be used to support multiple sun gears.
In a more specific embodiment of the present invention wherein a pawl is disposed between an inner peripheral surface of the sun gear and the axle for moving between an engaged position (wherein the sun gear is nonrotatably coupled to the axle) and a disengaged position (wherein the sun gear rotates relative to the axle), a pawl is retained to the axle such that an end of the pawl is biased radially outwardly to engage one of a plurality of ratchet teeth on the sun gear. To minimize the delay when switching the sun gear from the engaged state to the disengaged state, only one such pawl is provided, an the sun gear includes more than ten ratchet teeth (e.g., twelve) to ensure quick engagement between the pawl and one of the ratchet teeth. If the apparatus is used in a hub transmission of the type having a driver and a hub shell rotatably supported to the hub axle, wherein the sun gear mechanism is part of a planetary gear mechanism of the type described above, a roller clutch may be disposed between the ring gear and the hub shell to further reduce the delay when switching from one gear ratio to another gear ratio.
In another more specific embodiment of the present invention, a pawl control member may be provided for moving the pawl between the engaged position and the disengaged position. If the pawl control member is an elongated member disposed between the sun gear guide ring and the axle, then the sun gear guide ring not only stably supports the sun gear on the axle but also provides reinforcement to the pawl control member to minimize or eliminate the risk of bending or other damage to the pawl control member.
In another feature of the present invention directed to how the transmission is shifted from one gear to another gear, a clutch is provided for selecting the plurality of power transmission paths such that, when the clutch changes the power transmitting mechanism from a first intermediate speed transmission path having a first intermediate gear ratio to a second intermediate speed transmission path having a second intermediate gear ratio lower than the first intermediate gear ratio and adjacent to the first intermediate gear ratio, the clutch switches the power transmitting mechanism from the first intermediate speed transmission path to a third intermediate speed transmission path having a third intermediate gear ratio higher than the first intermediate gear ratio and less than a high speed gear ratio before switching the power transmitting mechanism to the second intermediate speed transmission path. Conversely, the clutch may be provided such that, when the clutch changes the power transmitting mechanism from a first intermediate speed transmission path having a first intermediate gear ratio to a second intermediate speed transmission path having a second intermediate gear ratio higher than the first intermediate gear ratio and adjacent to the first intermediate gear ratio, the clutch switches the power transmitting mechanism from the first intermediate speed transmission path to a third intermediate speed transmission path having a third intermediate gear ratio lower than the first intermediate gear ratio and higher than the low speed gear ratio before switching the power transmitting mechanism to the second intermediate speed transmission path.
In another feature of the present invention, an unbiased actuating member is used to operate the clutch while still providing the shift assist function noted above. In general, a shift control apparatus for a hub transmission includes an axle defining an axle axis; a pawl support rotating member rotatably supported around the axle axis; a pawl rotatably supported to the pawl support rotating member; a biasing mechanism for biasing the pawl in a radial direction; and a pawl control rotating member for controlling a radial position of the pawl. One of the pawl support rotating member and the pawl control rotating member includes a location for coupling to a shift control mechanism, and the other one of the pawl support rotating member and the pawl control rotating member includes a location for coupling to an actuating member. A spring is provided for biasing the pawl support rotating member and the pawl control rotating member in a rotational direction relative to each other, and a stopper is provided for holding the pawl support rotating member and the pawl control rotating member in a rotational position relative to each other. The actuating member rotates the pawl support rotating member and the pawl control rotating member in an opposite rotational direction relative to each other when resistance from the shift control mechanism overcomes a biasing force of the spring. More specifically, the axle defines an axle axis; a first rotating member is rotatably supported around the axle axis, wherein the first rotating member includes a location for coupling to a shift control mechanism; a second rotating member is rotatably supported around the axle axis; and a first spring is coupled between the first rotating member and the second rotating member for biasing the first rotating member and the second rotating member in a predetermined rotational direction relative to each other. A pawl support rotating member is rotatably supported around the axle axis, wherein the second rotating member is disposed between the first rotating member and the pawl support rotating member; a pawl is rotatably supported to the pawl support rotating member; a biasing mechanism biases the pawl in a radial direction; a first coupling member couples the first rotating member to the pawl support rotating member; and a pawl control rotating member controls a radial position of the pawl. An actuating member is rotatably supported around the axle axis for rotating the first rotating member; and a second coupling member couples the second rotating member, the pawl control rotating member and the actuating member for rotating the pawl control rotating member relative to the pawl support rotating member. This structure provides the shift assist function while providing no net bias to the actuating member.